Re: List manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg7422] Re: [mg7390] List manipulation*From*: penny at suu.edu (Des Penny)*Date*: Sat, 31 May 1997 15:07:37 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

>Hello, > > I have a list X={1,2,3,4,5,6,7,8}. How do I get a list of the >folllowing kind: > > S={{1,2,3,4}, {1,2,3,5}, {1,2,3,6}, .....}. > >S will have 8-choose-2 = 70 elements. Each element of S should have length >4. > > Is there any function which does such list making? Something of >the form > > ?????[list, n] > > Thanks in advance. > > > V. Nandagopal > School of Mathematics > Tata Institute of Fundamental Research > Colaba, Bombay 400 005, India > > e-mail: nandgopa at math.tifr.res.in Hi: This is more general that what you specifically asked for. The arguments to the function are: x= Supplied list n= Integer defining the number of fixed elements of x at the beginning of each sublist of the result. ============================== Clear[f] f[x_List,n_Integer]:= Module[{first, rest}, first=Take[x,n]; rest=Drop[x,n]; Map[Join[first,#]&,Map[List,rest]] ] ============================== Thus for your particular problem: In: x={1,2,3,4,5,6,7,8} f[x,3] Out: {{1,2,3,4},{1,2,3,5},{1,2,3,6},{1,2,3,7},{1,2,3,8}} If we only want 2 fixed elements of x in each sublist we have: In: f[{a,c,d,t,a,r},2] Out: {{a,c,d},{a,c,t},{a,c,a},{a,c,r}} Hope this helps. Cheers, Des Penny ------------------------------- Des Penny Physical Science Dept. Southern Utah University Cedar City, UT 84720 VOICE: (Office): (801) 586-7708 (Home) : (801) 586-2286 FAX: (801) 865-8051 e-mail: penny at suu.edu -------------------------------